As indicated in the foregoing Abstract, the system and method of this invention utilizes individual components of relatively small and transportable size which, when post-tensioned together in multiples form a prefabricated framing system. Although such components are tied together with tensioning wires, an important facet of my system is that the column or support spacing can be varied as required to meet building design considerations. Also, the system permits the addition or deletion of these basic components in any existing framework, this being an important consideration in many types of building structures such as, for example, hospitals and manufacturing plants. The latter are frequently subjected to changes in size and function and in the use of the instant novel scheme such is made possible. The individual components which are utilized in multiples for any building framework consist of a pair of horizontal intersecting beams cast integrally with a vertical column passing through the point of intersection of the horizontal beams; thus the components have four horizontal legs and two legs extending on each side vertically therefrom. In an alternate form, there may be four legs to the basic structure, positioned horizontally, and one extending leg positioned vertically thereto either downwardly therefrom or upwardly therefrom, thus comprising what might be termed a five-leg arrangement. These basic components form the basic structure of the ultimate building when tensioned and secured together in the manner hereinafter set forth. These individual elements are of reasonable size, i.e., such to meet the maximum load width of 12 feed which is generally imposed in most areas. Such limits the size of these components to about 16 feet along any axis, but meeting the 12 feet limit assuming the component is set on the transporter in a position where two of the legs thereof are angled to the horizontal. Despite this size limitation, when such basic components are utilized in forming the framing system of a given building, they are fully adequate for the erection of a framing system of a building of almost any reasonable size configuration.
There have been many attempts in the past to devise individual building components in an effort to achieve a pre-assembly in a building system representing the framework thereof. There have also been developments wherein both pre-tensioning and post-tensioning means have been utilized in this regard. However, the pre-tensioning media are not akin to this invention, simply because this improvement represents a scheme of post-tensioning media. Moreover, such post-tensioning systems as heretofore developed do not utilize the same method or means of achieving post-tensioning. In my system, when these elements are utilized in multiples they are first initially placed in position and held in such position by temporary restraining means. Concerning each leg of each structural element, the same is provided with an axial bore therethrough, this to accommodate a post-tensioning wire or wires therethrough and through adjacent members of the same type of structural element. Once wires are passed through each series of legs through the said bores, then the wires are tensioned by means to be later described, to thus stabilize and maintain the entire structure in permanent fashion.
Although certain prior art might approach resemblance to the individual structural elements which are herein utilized, the system and method of utilization is different and with no thought of a post-tensioning arrangement whereby, for example, a full room size framing of a given building, or multiples thereof, can be added or subtracted with regard to the completed building framework.
For example, the Dowling U.S. Pat. No. 3,466,823 utilizes a so-called tri-axial interlocking building element. These are interconnected via a non-rigid connector for interlocking the same together. The system of Dowling does not contemplate nor approach the novel scheme herein presented of elimination of such an interlock and of reliance entirely upon post-tensioned wires extending through the adjacent arms of a series of similar elements thus to sustain the entire load by post-tensioning means. Furthermore, a primary drawback of the Dowling system resides in the limitation in size of such components if they are to be transported over roadways to the construction site. Also, in the Dowling system, and as indicated, not only are welded connections and shim plates employed (at best an awkward procedure for assembly of the elements) but no means is provided for eliminating deflections in a cantilever, especially if one is added to the framing. The instant invention includes a means of controlling such deflection, and further, provides for the flexibility of this framing system relative to span variations. Although the said prior art item indicates the possible use of concrete as a material for the disclosed components, the reference indicated by that disclosure is primarily for the use of steel, aluminum, etc. -- indicating the necessity of fireproofing of such an assembly. It should also be noted that systems such as these do not permit framing variations, as in the instant invention, utilizing the structural elements which I employ. This means that such arrangements as in the system of the referred to patent could accommodate only about a 16 foot maximum column spacing in the building.
Other prior art is equally irrelevant: the Sardstrom et al. U.S. Pat. No. 3,846,946 illustrates the system of horizontal and vertical precast slabs or panels welded together at their juncture. In situ, concrete covers the welded joint. That system is thus also totally dissimilar. In Van Bijlevelt U.S. Pat. No. 3,295,266, the disclosed system is such that the resultant floor arrangement is made up of beams and slabs whereas in the instant case the floor and roof framing system comprises a two-way truss with integrally placed concrete floor slabs. Also, as to the latter patent, the beams and slabs are raised separately and assembled at respective floor levels whereas in my development the floor framing system, with integral floor slabs, can be raised as an entity.
Although Middendorf U.S. Pat. Nos. 3,029,490 and 3,270,471 appear to cover basic principles in post-tensioning an horizontally concrete member as a beam or slab, the involved tension members serve to limit deflection in the beam -- the greater the load on the beam the more tension must be exerted to limit deflection. In contrast, in my floor framing system comprising a two-way truss made up of structural elements, the bottom and top horizontal cords of the truss are held in compression through the action of the tensioning wires therein. The wires are in axial alignment with the cord members of the truss form and do not serve to prevent deflection of these members. Rather, the tension wires serve to hold together the components of the truss system, and also serve to prevent deflection or sagging of same.
The Middendorf (U.S. Pat. No. 3,255,558) and Dietrich (U.S. Pat. No. 3,696,574) patents are of a related nature to the other prior art mentioned above and involve fastening system not equivalent to my post-tensioned arrangement.
The system of this invention is thus presented as an entirely novel system, means and method unique to the prior art for prefabrication of structural elements, transportation to the site, erection at the site and after temporary stabilizing and securing in position, post-tensioning of the entire assembly to achieve a permanent building framing; also, with such an assembled structure, even when completed as filled with modular units to be inserted therein, the same is subject to enlargement or reduction in size, room by room or in multiples of rooms.